1. Field of the Invention
The present invention relates to a method and apparatus for controlling a transfer voltage of an image forming apparatus, and more particularly, to a method and apparatus which measures the thickness of a supplied sheet to thereby vary and control the transfer voltage.
The present application is based on Korean priority application 97-41192 which is incorporated herein by reference.
2. Description of the Related Art
An image forming apparatus reproduces characters or images onto a recording medium according to transferred character or picture image data signals, and generally includes a photoreceptor member (e.g., a photoreceptor drum or a photoreceptor belt) for forming a latent electrostatic image, a charging means for charging the photoreceptor member, an exposing unit for forming a latent electrostatic image having a predetermined pattern by scanning light onto the charged photoreceptor member, a developing unit for developing the latent electrostatic image by supplying a developing medium (e.g., a toner or a developer liquid) on the exposed latent electrostatic image, and a transfer unit for transferring the developed image to the recording medium by applying pressure or heat.
Referring to FIG. 1 showing a general image forming apparatus, the image forming apparatus including a photoreceptor belt 104 installed to be capable of moving circulatively by first, second and third belt rollers 101, 102 and 103, a discharger 105 for removing charges remaining on the photoreceptor belt 104, a charger 106 for newly generating the charges on the photoreceptor belt 104, exposing units 107, 108, 109 and 110 each having a laser scanning unit (not shown) for scanning a laser beam for the purpose of selectively discharging the image forming portion of the photoreceptor belt 104 to be formed, into an image-shaped pattern, developing units 111, 112, 113 and 114 for respective colors yellow (Y), magenta (M), cyan (C) and black (K), for developing the latent electrostatic image formed on the photoreceptor belt 104, a drier 115 for drying the developer liquid supplied to the latent electrostatic image, and a transfer unit 116 for transferring an arbitrarily developed image formed on the photoreceptor belt 104 to a recording medium 117 such as a sheet of paper or a film.
Here, the developing unit 111 includes a developing roller 111a for coating the developer liquid on the photoreceptor belt 104, a developer liquid supplier 111b for supplying the developer liquid to the developing roller 111a, a cleaning roller 111c for removing the developer liquid embedded on the rear surface of the developing roller 111a, first and second squeegee rollers 111d and 111e for removing the developer liquid remaining in the photoreceptor belt 104, first and second blades 111f and 111g for removing the developer liquid embedded on the first and second squeegee rollers 111d and 111e, and a developer liquid recovery container 111h for recovering the developer liquid removed by the cleaning roller 111c and blades 111f and 111g. The drier 115 includes a heating roller 115h for drying the developer liquid embedded on the photoreceptor belt 104. The transfer unit 116 includes a transfer roller 116t pressing closely against the first belt roller 101 and rotating reciprocally thereto, with the photoreceptor belt 104 interposed between the transfer roller 116t and the first belt roller 101 for receiving the image from the photoreceptor belt 104, and a fixing roller 116p pressing closely against the transfer roller 116t and rotating reciprocally thereto for fixing the image transferred to the transfer roller 116t on the recording sheet 117 interposed therebetween.
In the image forming apparatus having the aforementioned configuration, conventionally the transfer conditions are controlled by detecting only the ambient temperature and humidity. Thus, if the thicknesses of sheets used are different (e.g., if the sheets become thicker) the transfer efficiency is lowered, thereby precluding the attainment of a good quality image. If a transfer voltage is increased to a predetermined level or higher in order to solve this problem, a photoreceptor belt may be damaged by arc discharge and a great deal of ozone (O.sub.3) may be generated.